JWK

To smaller tires/wheels, like 650b. They quote "27.5", so I assume they are talking of the typical 42mm and 47mm tires. I don't get it. I've looked over everything on the frame geometry. 70mm bottom bracket drop. Should be no problem with pedal sc****, especially with my 170mm crank arms.

I mean, sure it would look "funny" with those big clearances on the frame, but what would be an actual problem? Salsa just states those wheels are significantly smaller than the 29er wheels the bike was designed for.

So no real reason given. What exactly happens when you put a 650b 42mm set on, or a 700c 28mm set? I know a number of people own a cutthroat here, so I was hoping someone could explain this to me and tell me the smallest tire they run on their bike when they want to do a road ride.

Thanks for any help understanding this. I'm still thinking seriously of getting a cutthroat, but with the cost it would definitely be a one-bike situation for awhile.

JWK

Wow, I can't believe the editor wouldn't let me put in "pedal s-c-r-a-p-e" I can't even figure that one out!

dsaul

It just won't have the ground clearance that Surly intended. Theoretically, the outer diameter of a 29 x 2.2 tire is 733mm and the outer diameter of a 27.5 x 47 tire is 678mm, so the bottom bracket will be 27.5mm closer to the ground. That leaves you with 269mm from the center of the bottom bracket to the ground. I built my first gravel frame with 80mm of drop and 700 x 35 tires, which left me with 266mm to the ground. On singletrack, I would occasionally get pedal strikes on roots and rocks. I built my current frame with 60mm of drop and 27.5 x 47mm tires and have no problems with pedal strike on singletrack.

As long as you are aware of the possible pedal strike issues, there should be no problem with running a 27.5 x 47 or 700 x 35 tire on that frame. I would not recommend going any smaller than those tire sizes for off road riding. 700 x 28 will be fine on the road.

Elvo

Yup definitely pedal strike concerns. The cutthroat is designed as a drop bar MTB with a ~12"+ bb height. I would go with at least 10.5" minimum bb height for road

JWK

OK, it makes sense that Salsa would only be addressing off-road biking. So I can't see a problem for me for my use. For road use I would use no smaller than a 700c x 38mm or 650b x 42mm. BMC Road+ designed for 650b x 47mm has a BB drop of 73mm and Mike Varley told me it would be no problem using 42mm tires. Plus, with my 170mm crank arms I gain about 2 inches of clearance for pedal strike compared to most bikes in my size (58, usually).

Thanks for the info.

wheelsmcgee

Last four letters...it’s kind of ridiculous.

JWK

Oh, I see. Kinda weird and funny. Oh well, "pedal strike" is the better, standard phrase anyway. My mind was just blanking.

Caliper

I'd look at what happens to the trail numbers (Steering). Dropping the tire size will reduce the trail at the ground and make the bike a bit less stable. "Cannot" may be a strong word though since it sounds like the 650B would fit and ride just that it might ride differently from how it does with the larger 700c/29er wheels/tires. I know in some of Salsa's other responses they have said that the tire won't have proper clearance and stuff so I'm not thinking that's the issue here.

There is a Cutthroat group on Facebook, you may try asking there and see who's running 650B's. Of course, why you would want to run smaller tires confuses me...

I think people today are far too worried about pedal strike anyways. Lower BB's feel great, just don't be silly and be aware of where your pedals are.

chas58

That is not what it is designed for, but you can do it. Its just going to change things a bit (pedal strike, trail). Its a pretty stable bike, so a little less trail isn't going to hurt much, and you don't mind the pedal strike or lower bottom bracket. It will make the bike descend a little better.

kevrider

a couple of things...
- as mentioned, it’s not just pedal strikes, going to 650b would change your rake and trail dramatically, affecting handling and not in a good way... you can probably calculate the changes online, the bike would be far less stable
- 170mm cranks will not buy 2” if clearance, pedal strikes happen while going straight, most larger bikes have 175mm crankarms, that’s 1/4 of an inch
- 650b on this bike does not make sense... people convert gravel bikes to 650b because it is necessary in order to fit a wider tire, 47-50mm, for many gravel-specific frames. with cutthroat being a mtn bike, obviously that is not true, so downsizing the rim offers no advantage... for the road, 700x35mm gravel tires would be great

kevrider

i’m thinking the opposite.

chas58

You are right, its kind of a mixed bag. In general, lowering the BB height and center of gravity will make the bike more stable in fast loose conditions. Less trail will make it a little more lively. But in my experience its not a lot, and that is a fairly stable bike.

kevrider

I agree that it is USUALLY not a lot... I converted by gravel bike to 650b. but he is talking about a 29er. I think 29 x 2.2 to 27.5 x 47mm is a bigger than usual change. most of the time, people go with a smaller diameter to an increased width, which reduced the change in total circumference. the OP is going smaller AND skinnier, which more drastic and offers no obvious profit. he can just put a 40mm tire on the stock rims.

@JWK... that would be the play... consider 700 x 40-45mm, then you won't often have need to swap back to the mtn bike tires, unless you really want to have fun.