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Mid 80s Trek 720 questions - Max tires and fit?

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Mid 80s Trek 720 questions - Max tires and fit?

Old 07-03-20, 10:32 AM
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Mid 80s Trek 720 questions - Max tires and fit?

I'm looking at some mid 80s Trek 720 bikes. My purpose is for comfortable all day road riding on very rough roads. Touring load not required. I would need to carry quite a bit of water at times, some food, clothing for weather, etc. I guess sort of what you might need on a brevit, except for the water part. My understanding is that there is water available on brevits. There are rides I can take here in central Maine where I cannot count on finding water, so having to carry a gallon or more at the start is very likely. Max total weight could get up to 250 lbs. I weigh 210.

I am just a hair under 6' with a 34" inseam. From what I can gather, I would be looking for a 22.5" frame. Is this correct?
What is the max tire size for the 720? I see some had 27" wheels, some 700c, even in the mid 80s. Were the frames actually different, or did they just put different wheels in? In any case, what can you fit in there using a 700c? I'm hoping for 38mm tires without fenders.

So I'm wondering if the frame will be too noodley with 215 - 235 lbs. on top of it, and what I can expect for tire clearance.

I've got a Univega Alpina from '97 I could build up, but that's a totally different kind of thing (obviously) and will be for a different thread. I'm just throwing it in there in case it would fit my purpose better than the 720.

Thanks for any help.

Last edited by JWK; 07-03-20 at 10:33 AM. Reason: model number corrrection
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Old 07-04-20, 08:15 AM
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Old 07-04-20, 09:30 AM
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Size-wise, at 6ft I'd be looking for 24" frames, unless you like large standover and have specific ideas about what you'd like to do with the stem. I'm 5'11" and use a 24" Trek frame with more than a fistful of seatpost showing.

Depending on brakes being used, you can probably get away with a conversion to 700c from 27", and get a little more tire clearance that way. I'll let the 720 experts here weigh in on exactly how much clearance you'll get, but I think you'd probably be able to go at least 35mm without fenders, and 38mm doesn't sound too crazy to me.

Since you're not looking to do heavy loaded touring, take a look at the 6xx series from Trek in the early 80's, too. 531 main triangles and sport/touring geometry. Might be a more lively ride than the long wheelbase 720 would give you and doesn't command the precious pricing of 720s. I have a pre-cantilever '83 Trek 620 that fit 35mm tires at 700c, but no more room than that. Great frame, currently being modded by @gugie to convert to 650B.

For sizing concerns, here's what a 24" '83 620 looks like for someone at 5'11":
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Old 07-04-20, 09:41 AM
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Maybe try sending a pm to one of the moderators to get the title of your thread changed from 920 to 720. Or just start a new thread. I'm sure you'd get more responses that way. I think you're probably looking at a 24" frame being a better fit than a 22" at your height.
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Old 07-04-20, 10:02 AM
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Changed title to "720"
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Old 07-04-20, 12:11 PM
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Originally Posted by Homebrew01 View Post
Changed title to "720"
Thank You!! OMG, I didn't even notice that. No wonder I went a day without a response...
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Old 07-04-20, 12:16 PM
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Originally Posted by bear_a_bug View Post
Size-wise, at 6ft I'd be looking for 24" frames, unless you like large standover and have specific ideas about what you'd like to do with the stem. I'm 5'11" and use a 24" Trek frame with more than a fistful of seatpost showing.

Depending on brakes being used, you can probably get away with a conversion to 700c from 27", and get a little more tire clearance that way. I'll let the 720 experts here weigh in on exactly how much clearance you'll get, but I think you'd probably be able to go at least 35mm without fenders, and 38mm doesn't sound too crazy to me.

Since you're not looking to do heavy loaded touring, take a look at the 6xx series from Trek in the early 80's, too. 531 main triangles and sport/touring geometry. Might be a more lively ride than the long wheelbase 720 would give you and doesn't command the precious pricing of 720s. I have a pre-cantilever '83 Trek 620 that fit 35mm tires at 700c, but no more room than that. Great frame, currently being modded by @gugie to convert to 650B.
Thanks! That's very helpful. Yes, Given your description and pic, I'm certain I'm looking at 24". Also, it sounds like I would prefer a 620. What do you think you will fit with the 650b conversion? 42mm?
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Old 07-04-20, 12:21 PM
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Just pulled the trigger on an 85 720 from a forum member here and we had a lot of discussion about clearance. All 84/85 720s (unless purchased as a frame) came with 27” wheels. With 700c, the cantis that came with this bike will adjust easily enough to work, according to every account I’ve read. With 700c you can absolutely fit 35s, and most likely 38s without fenders, but not sure about that one.

At 5’11” I find 58cm frames just a hair large but near perfect. I opted for the 22.5” trek. Haven’t gotten to ride it yet though.
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Old 07-04-20, 12:31 PM
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Originally Posted by JWK View Post
Thanks! That's very helpful. Yes, Given your description and pic, I'm certain I'm looking at 24". Also, it sounds like I would prefer a 620. What do you think you will fit with the 650b conversion? 42mm?
fyi - You won't be able to convert to 650b if you get a 1984 or 1985 620 because both use canti brakes (unless you get the posts moved down) - 700c will work though. 700c conversion is also easier with the 1985 620 because it used brakes that had more internal adjustability than the Dia Compes used on the 1984. (But I did get my 1984 620 with Dia Compe brakes to work with 700c).

As mentioned previously, the 1983 620 uses caliper brakes so 650b is possible. 42mm without fenders is a maybe with 650b.

Last edited by jlaw; 07-04-20 at 12:39 PM.
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Old 07-04-20, 12:41 PM
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Most of the touring bikes back then used 27x1 1/4" rims/tires. If you find one with a 700C someone probably changed the wheels or had something built. If you find a frame without canti bosses you can put whatever you like on it, 650b (check clearances and steering) or 700c or 27". If you get one with Canti's it will limit you to 700c or 27" unless you want to modify the frame or have it modified.
Get the frame then worry about tire size. Decide if you want fenders or not, as that will influence the tire size also.
The 6xx aren't automatically sport touring frames either. If you find a frame , check the year and then the old catalogs to see what the frame specs are, one year the trek 620 had the same chainstay length as the 720. most others years they were shorter. The 520's usually had short chainstays compared to full touring frames. The later 600/610 series make good 650b conversion frames also.
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Old 07-04-20, 01:01 PM
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Originally Posted by JWK View Post
Thanks! That's very helpful. Yes, Given your description and pic, I'm certain I'm looking at 24". Also, it sounds like I would prefer a 620. What do you think you will fit with the 650b conversion? 42mm?
650Bx42mm worked just fine without modification, though I dimpled the chainstays a hair just to let me sleep easier at night.

Also, though the later years had cantilever brakes, I think you COULD convert to 650B, you'd just have to cease using the existing canti studs and use calipers. Looks goofy, but it would probably work.

If you're not dead-set on a Trek, I (and others here) have had great success with late 70s/early 80s Fuji S12-S frames. With their easy clearances and geometry, they almost seem to beg for conversion
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Old 07-04-20, 01:23 PM
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I agree with others who say try for the 24 inch Trek. I have legs like yours and have a 24 inch 1985 620. If you are not going to use panniers, you might also consider the 710/610 frames which are a little shorter in the back.
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Old 07-04-20, 03:47 PM
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Original owner of a 1982 Trek 720. Still my daily driver. At 5'9", 1.75m, the 22in/56cm frame fits fine.

Had 27 inch/ISO 630 rims with cantilevers. Maximum tire width with fenders was 28mm.

Converted to ISO 622 rims. Cantis did NOT work with reduction in radius. Removed canti studs and
went with 610mm reach centerpulls front and rear. Max tire width with fenders was 33mm.

Fork developed crack a few years ago. Replaced with higher offset fork and went to 650B/ISO 584.
Max width with fenders is now 44mm. ( This is actual width, not width labeled on tire. The current
tires are labeled 50-584/27.5x2.00. ) Using Sturmey Archer drum brakes front and rear. A 75mm
centerpull will work with 650B on the rear wheel. However, due to a slightly higher axle-to-crown
height on the new fork, a 75mm centerpull would not currently work on the front. That's OK since the
drum brakes work much better than any rim brake the bike has had. A 75mm reach centerpull
will fit 650b and the original fork.

The current setup handles great. 44mm tires give all the comfort one might imagine. Lower trail
improved handling, especially at low speeds and loaded with groceries. Figure I carry 30 lb./ 14kg of
goods along with my own 170 lb/ 77kg. Smooth and steady ride. NOT fast at all.

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Old 07-04-20, 05:49 PM
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Originally Posted by JWK View Post
I'm looking at some mid 80s Trek 720 bikes. My purpose is for comfortable all day road riding on very rough roads. Touring load not required. I would need to carry quite a bit of water at times, some food, clothing for weather, etc. I guess sort of what you might need on a brevit, except for the water part. My understanding is that there is water available on brevits. There are rides I can take here in central Maine where I cannot count on finding water, so having to carry a gallon or more at the start is very likely. Max total weight could get up to 250 lbs. I weigh 210.

I am just a hair under 6' with a 34" inseam. From what I can gather, I would be looking for a 22.5" frame. Is this correct?
What is the max tire size for the 720? I see some had 27" wheels, some 700c, even in the mid 80s. Were the frames actually different, or did they just put different wheels in? In any case, what can you fit in there using a 700c? I'm hoping for 38mm tires without fenders.

So I'm wondering if the frame will be too noodley with 215 - 235 lbs. on top of it, and what I can expect for tire clearance.

I've got a Univega Alpina from '97 I could build up, but that's a totally different kind of thing (obviously) and will be for a different thread. I'm just throwing it in there in case it would fit my purpose better than the 720.

Thanks for any help.
I just got a 1982 720 sized 20.5" or 52 cm. I'm just under 5'6" and about 190#. I expect the main triangle to be stiffer than most 531 db road bikes, because the downtube has thicker walls than most others. Same for nearly all Treks of the era. The seatstays are quite long at 47 cm. This is mainly for heel clearance relative to the rear panniers. From the inception they were known as long distance tourers that could carry all that was needed for self-supported travel on two wheels. There may be some noodliness, but I don't know yet. Mine won't be ready to ride for a few weeks. I have another Trek, a 1984 610, which is not noodly and if anything is too stiff, in my opinion.

It looks to me like I can use 700c up to about 35 mm wide. I think 650b x 42 will be too fat, and I'm not sure what you can do for brakes when you have cantilever posts anyway. My first build will be 27x1 ¼ rims with either 1 ¼ or 1 ⅜" width tires. If I take the wheels from my 610 there will be 700 x 32, at least to start with. But I don't share the common belief that original tires are inadequate for touring, at least when the tireks are new.

But with my frame being set up for caliper brakes rather than cantilevers, it is inherently more versatile. With long enough calipers I could go to 650b, though I haven't researched exactly what that would take.

There are a lot of modern touring racks, including fronts, which can take large panniers and carry a lot more weight than the ones available in the mid 1980s. They can nearly all be attached to that frame using theeyeleys that are provided. If I was a tourist, the only thing I think might be missing is a pair of mid-fork mounts for front low-rider panniers. It used to be common to take a frame to a framebuilder to have touring braze-ons added. At the same time you should probably look at getting the rear triangles cold-set and aligned to accept 130 mm wheels. That lets you convert to 10 speed gearing o 3x10 gearing and indexing. But that's all for you to think through.
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Old 07-05-20, 07:18 AM
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Originally Posted by JWK View Post
What is the max tire size for the 720? I see some had 27" wheels, some 700c, even in the mid 80s. Were the frames actually different, or did they just put different wheels in? In any case, what can you fit in there using a 700c? I'm hoping for 38mm tires without fenders.
The first 720s were built to use 27" wheels, as the model was intended for loaded touring, and 700C was not yet common in rural areas. Later ones used 700C wheels. The only difference was where the cantilever brake bosses were brazed to the frame and fork. Depending on the specific brake used, a frame built for 27" wheels might have trouble with 700C wheels if the pads can't be lowered enough to reach the rim.

I run 27 x 1-1/4" (32mm) tires on my 720. There's room for wider tires, especially if you don't have fenders.
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Old 07-05-20, 11:51 AM
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Originally Posted by JWK View Post
My purpose is for comfortable all day road riding on very rough roads.
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Old 07-05-20, 07:19 PM
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Originally Posted by JWK View Post
I'm looking at some mid 80s Trek 720 bikes.
This is kind of intriguing... Not that the 720 is particularly rare bike- but there were only 8,000 or so made over the course of 4 years more than 35 years ago. They're around- but I'm intrigued by a gaggle of them hanging around out there.

There was a hybrid bike that was given the model name of 720 in the early 90s- a completely different bike, a decent bike- but not 'flagship class' like the early/mid 80s 720. If this is the hybrid 720- then frame sizing gets a little goofy with the higher bottom bracket and sloping top tube.

You might wish to post pix of a bike similar to the bikes you're looking at (or the bikes you're looking at)- just to make sure people can give you more accurate information.

This is my 1985 Trek 720. It's running 700 x 35 tires with SKS P45 Chromoplastic fenders. Larger tires will not fit with fenders, but you might be able to get a 38 under the fork crown if you try.

IMG_2377 by Dave The Golden Boy, on Flickr
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Old 07-07-20, 05:48 AM
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Originally Posted by JWK View Post
I'm looking at some mid 80s Trek 720 bikes. My purpose is for comfortable all day road riding on very rough roads. Touring load not required. I would need to carry quite a bit of water at times, some food, clothing for weather, etc. I guess sort of what you might need on a brevit, except for the water part. My understanding is that there is water available on brevits. There are rides I can take here in central Maine where I cannot count on finding water, so having to carry a gallon or more at the start is very likely. Max total weight could get up to 250 lbs. I weigh 210.

I am just a hair under 6' with a 34" inseam. From what I can gather, I would be looking for a 22.5" frame. Is this correct?
What is the max tire size for the 720? I see some had 27" wheels, some 700c, even in the mid 80s. Were the frames actually different, or did they just put different wheels in? In any case, what can you fit in there using a 700c? I'm hoping for 38mm tires without fenders.

So I'm wondering if the frame will be too noodley with 215 - 235 lbs. on top of it, and what I can expect for tire clearance.

I've got a Univega Alpina from '97 I could build up, but that's a totally different kind of thing (obviously) and will be for a different thread. I'm just throwing it in there in case it would fit my purpose better than the 720.

Thanks for any help.
I have been measuring up my 1982 52 cm bike. I think the spacing between the stays and the fork blades could accommodate tires up to 36 mm or so, without fenders and with very good frame alignment. For noodliness, I really don't know what that means. Do you have an example of another frame that gave you that worry? The 720s were designed to handle long-distance self-supporting touring loads of the day. The tubes are claimed to be standard Reynolds 531 double butted top tube 8/5/8, single butted 8/6 seat tube and double butted 1.0/0.7/1.0 down tube. Diameters are standard, 1" TT, and 1 ⅛" ST and DT. Compared to existing and highly-respected randonneuring bikes dating back to about 1950 (notably the Herse and Singers that Jan Heine has written about, the tubes are very similar if not perhaps a little thicker in the walls - hence stiffer.

So these are the reasons I wanted one - to make a town/training/rando bike without paying Peter Weigle or Alex Singer prices. I appreciate the value of flex designed into the frame, but I don't know if another person would interpret that as noodliness.
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Old 07-07-20, 11:14 AM
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You also need to factor in the 47cm chainstays (as well as the overall frame size) into the equation.

When people talk about the 720 and the 85 620, the words "flexy" and "noodley" often come up.

I'm not a very powerful rider- even when I was at my strongest, however I could make my 620 auto shift by really standing on it. I think my 720 is more stiff and I haven't experienced that level of "give" on that bike.
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Old 07-08-20, 10:14 PM
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I ride a 24” 720, an ‘83.
I’ve found it to be flexible when fully loaded with camping gear, tent, stove, sleeping bag, etc.

But that same flexibility when fully loaded means it’s a JOY on gravel. You get it up to a certain speed and the frame absolutely floats along. It’s pretty amazing.

My ‘83 has cantilevers so you wouldn’t be able to do 650B, but I believe I could adjust them to 700c without to much trouble.

As it sits it has 27” rims, 1 1/4 tires (32/35mm) and it’s wearing fenders. Without those fenders you could go even bigger, and a switch to 700c would net even more mm’s of clearance. I also have an ‘84 520 and an ‘84 620, the tire clearance on those frames is a lot smaller, 28mm with fenders, 32mm without. 32mm works pretty great on gravel though, so while it’s a little less, I would say it’s perfectly adequate. If you have one available in your size, I’d snap it up, but there are a LOT of old steel that would make a sweet gravel bike.

I think it’s a perfect frame for your mission, I love mine on gravel roads.

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Old 07-09-20, 06:03 AM
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I'm in agreement with pretty much everyone here

Like goldenboy , I have an '85 720, same color and size. I don't do fenders, so 700c 35mm Schwalbe Marathon Supremes fit with plenty of room to spare. And, by the way, it's a great tire. Got them 300 miles before a 2k mile tour last summer and I put on another K or so since. Not one flat. The 720 is the smoothest bike I've ever ridden.
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Old 07-09-20, 07:46 AM
  #22  
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I'm a short 6' and went with 22.5"
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Old 07-09-20, 07:52 AM
  #23  
Chr0m0ly 
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Originally Posted by JWK View Post
I'm looking at some mid 80s Trek 720 bikes. My purpose is for comfortable all day road riding on very rough roads. Touring load not required. I would need to carry quite a bit of water at times, some food, clothing for weather, etc. I guess sort of what you might need on a brevit, except for the water part. My understanding is that there is water available on brevits. There are rides I can take here in central Maine where I cannot count on finding water, so having to carry a gallon or more at the start is very likely. Max total weight could get up to 250 lbs. I weigh 210.

I am just a hair under 6' with a 34" inseam. From what I can gather, I would be looking for a 22.5" frame. Is this correct?
What is the max tire size for the 720? I see some had 27" wheels, some 700c, even in the mid 80s. Were the frames actually different, or did they just put different wheels in? In any case, what can you fit in there using a 700c? I'm hoping for 38mm tires without fenders.

So I'm wondering if the frame will be too noodley with 215 - 235 lbs. on top of it, and what I can expect for tire clearance.

I've got a Univega Alpina from '97 I could build up, but that's a totally different kind of thing (obviously) and will be for a different thread. I'm just throwing it in there in case it would fit my purpose better than the 720.

Thanks for any help.
If frame flex is a concern, I’d look at Miyata 610 frames and also Cannondale ST frames. I can tell you from experience that an ‘84 Miyata 610 will take up to a 700x40mm tire.
The Cannondale ST frames have a bit less tire clearance at the chain stays, but around ‘88 or ‘89 they started dimpling them. With the dimple you can fit 32mm tires.
Another forum member has an earlier Cdale and reports having a 32mm in an undimpled frame, so it appears to be variable. That’s not surprising in hand made production frames. I had a Cannondale Crit, a Black Lightning, they normally only fit 23 or maybe 25mm tires, and that one would take 28mm tires.

Last edited by Chr0m0ly; 07-09-20 at 08:19 AM.
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Old 07-09-20, 12:32 PM
  #24  
ryansu 
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My 2 cents I am 5' 10 ish with a 30" inseam and a loooooong torso and ride a 22.5/57cm 1987 Trek 520. I *think* you want something a bit larger for your inseam. I am running the 27 inch stock wheels with 27 x 1 1/4 tires and they fit good and I think the Sand Canyon 27 x 1 3/8 tires I run on my 87 Nishiki Cresta would work on the bike as well. This year of 520 has Reynolds 531 main tubes and I love the smoothness of the ride. Based on Vintage Trek it appears the 720 road bike was made in 82 to 85


87 trek 520

Last edited by ryansu; 07-09-20 at 12:44 PM.
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Old 07-15-20, 09:09 PM
  #25  
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I just did a frame up rebuild of a 1984 Trek 720. Except for the brakes and levers I used all the parts from a donor 2013 Trek 520. I cold set the dropouts to fit the 700c wheels. Schwalbe Marathon 35c tires fit with room to spare, i left the fenders off for now.
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