Yen

Can you stand another post about LHT sizing? I'm scrounging the forums and using Google to read anything I can about the sizing of this bike. As I've stated in my other post about the LHT as an all-around bike, I prefer riding more upright than stretched out. Not as upright as a hybrid, but less stretched out than even my Roubaix which has a comfortable geometry as road bikes go. I enjoy a "check-out-the-scenery" position.

Last weekend I test rode the 54cm LHT. I loved it. It is *very* close to meeting my ideal with out any changes whatsoever. Since then, I've been doing a lot of research and studying the size chart against my measurements and those of the Roubaix, just to be certain that the 54cm is right for me, and I noticed something interesting on the LHT size chart.

While the ST and TT lengths and SO height continue to increase with each larger size, the length of the HT drops from 182mm on the 54 to 152mm on the 56. Therefore, on the 56, while the ST would be taller and the TT longer, the HT would be shorter. I would be much more stretched out and further adjustments would be needed. This seems to point directly to the 54cm frame for me. Or am I missing something???

I got these numbers from the size chart at the Surly site. Is the decrease in HT length typical on touring bikes?

BTW, my inseam is 33" (bare feet to PB).

brianmcg123

That is why they invented spacers.

But when you look at the LHT and compare geometries between sizes it really doesn't do you any good when comparing the 26" wheel models to the 700c models. They are pretty much compelety different bikes since they have different wheel sizes.

Erick L

The 54cm uses 26" wheels and the 56cm uses 700c. I suppose the HT is shorter to accomodate the larger wheel.

Yen

Does that mean that a 56cm might feel very much the same as the 54?

Yen

Thanks.... after discussing this a while longer, we figured there had to be a correlation between the shorter HT and the larger wheel.

seeker333

The bsd on 26" is 559mm nominal. 622 on 700c. so (622-559)/2=31.50mm. For same diameter tire, front axle will be 31.5mm higher from ground on 700c. If you look at Surly chart you will note the BB drop is 31mm greater on 700c wheeled versions to compensate for this difference. Keeps BB height constant - a design goal being to keep BB and rest of bike and rider at lower CG for stability. High BB simply not needed on tourer, due to lack of sharp, pedaled turns of racers or the uneven terrain of mtb.

Fork on 26 is 376mm a-t-c, on 700c is 390mm. 700c fork is 14mm taller from axle to crown.

HT angle is 71 /72 deg, respectively. Just to make my life easier lets call em the same.

So, 32+12=44mm - 56cm is therefore 44mm total taller than 54cm LHT from ground to fork crown with wheel mounted and tire of same size.

Factor in HT length - 182 vs 152. 56cm is 30mm shorter. But starts off 44mm higher due to wheel diam and fork, Ends up 44-30= 14mm taller to top of headtube with same stack height headsets installed.

So, compared to 54cm LHT, the 56 is 20mm taller in seat tube length and height at seat post clamp and 14mm taller at top of the headset.

You can usually compensate more than this by adjusting saddle height and fore/aft position, stem height with spacers, bar reach with combination of stem length and bar choice. Pick the size that gives you the greatest range of adjustment for your body in terms of reach and standover. If you have unusual physical proportions such as short leg/ long torso or vice versa, then this complicates the fit process. In extreme cases a custom frame is required.

Bear in mind that Surly geometry based on 26x1.25 or 700x28 tires. If you get a 54 and mount 2" Schwable tires you'll increase standover height ~15-20mm, depending on tires. Same for 700c to a lesser extent.

If you get 54, I doubt you'll be happy with 1.25" tires. I have found 1.5" go flat far less, last much longer, and ride a little smoother - they're a heavier tire and have more rubber in the tread area. And if you go off pavement much at all you need mtb size tires, about 2".

treebound 

If you really want to scratch your head compare the bottom bracket drop dimensions between the 54 and 56 sized frames.

This makes me really want to test sit or test ride one in each size to really feel the difference.

HardyWeinberg

I am using 2.0" big apples on my 54 and I love it. LOVE it.

MtTabor

I just bought a 54cm LHT yesterday, after test-riding both the 54cm and the 56cm. My PBH is right about the same as yours. These are two totally different bikes, judging by the geometries. The 56cm had me too stretched out, and no amount of stem-swapping was able to correct it. The 54 has the right TT length, and I think I'll warm to the 26" tires.

Bicycle dad

While I do not recall my inseam measurement I can say this.

I have a 58cm LHT and ride a 56cm Allez Pro road bike.

The only thing I did to the LHT was put a zero set back seat post (thomson) and I run I think two spacers under the stem on the front. The LHT is much more upright than the Allez and I do not feel stretched on ether bike but the drop on the Allez is way more aggressive.

Bacciagalupe

42-54cm LHT's use 26" wheels. 56cm and up use 700c. So yes, they are slightly different bikes. I assume they're going to ride very similarly though.


One thing to keep in mind about sizing and fit, though, is that how something feels for 15 minutes will be very different after 30 minutes, which is different than 3 hours, and 8 hours is a totally different ball of wax.

I do think that a test ride will give you a very basic guide, at least enough to know "54 fits and 56 does not" if you have a good LBS. Don't be surprised though if you feel the itch to tweak your setup as you do longer rides on the bike.

Yen

Thanks everyone.

I'm still leaning toward the 54cm, but I'd like to find a 56cm just to test for comparison. However, I liked the lower feeling on the 54 with the 26" wheels! It felt stable and secure for riding in traffic. And, the TT measurement of the 56 is almost an inch longer than the TT on my Roubaix which I wish was shorter. The Surly site says to use the TT measurement first, then the SO height, and also to base it on a current bike that fits well.

seeker333

The actual BB height on all LHTs is exactly the same for a given tire size, regardless of wheel diameter.

Read first paragraph of my last post, immediately above your last post for simple explanation.

seeker333

I've ridden all sizes from 1.0 to 2.2", and also much prefer the larger tires. They ride better and make life simpler.

I think this may be one explanation for comments I've read about LHT's "running large". I haven't read of them "running small".

I think folks try them on, with stock 1.5s, or read geometry table, which is apparently based on 1.25" tires. They pick a size, buy one, install 2" tires, and now because the TT is jammed into their gonads they think "huh, these things run large, maybe i shoulda got one size smaller".

I believe a touring bike should be fit a little like a mtb, with a little more standover clearance for the uneven surfaces of off-pavement conditions, plus the ability to quickly and easily reach the ground to balance a touring load, with long pants, etc on.

You can get by with an inch clearance on a dedicated road bike, but you need a bit more room for a tourer. Add in the effect of larger tires needed for unpaved terrain, and you find yourself needing to drop down a size.

Yen

Thank you.... that explanation helps me a LOT. I was wondering why I've read that the LHT sizing runs large, yet see so many people who bought a size larger than their true road bike! Your explanation of the tires makes sense, and also helps me determine the SO height best for me. The SO height on the 56cm would give me only 1" clearance which is a little too close for my comfort. I'd prefer more, and should leave room in case I do add larger tires later.

El Pelon

This is a good thread with a lot of useful information for anyone considering the LHT. Well done.

Yen

And I thought I was asking a dumb question....

treebound 

Ah, somehow I missed that, thanks.