Bike Performance on Wheelbase

Krank
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Bike Performance on Wheelbase

Postby Krank » Sat Nov 03, 2012 10:19 am

How does wheelbase affect bike performance?

I know that longer wheelbase improves stability, but what does a longer wheelbase adversely affect?

Likewise for a shorter wheelbase?

How can you calculate what the optimal wheelbase is for your riding style and body dimensions?


Krank

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Re: Bike Performance on Wheelbase

Postby high_tea » Sat Nov 03, 2012 10:36 am

My highly subjective and inexpert option:

shorter = sharper steering.
longer = more stable.

All things being equal, of course.

Long long wheelbases, like cargo bikes and tandems are harder to get over bumps and around tight corners. For the sort of variations we're talking about with single bikes (100mm or so*) I suspect the big difference is how the bike feels. A couple of other things have bugged me about shorter wheelbases over the years:

- heel clearance if I use panniers. Longer chainstays fix this, which affect the wheelbase but the requirement isn't a a long wheelbase, it just pans out that way.
- toe clearance if I use mudguards. Same thing, what I want is more fork offset and/or a "slacker" headtube. This too happens to affect the wheelbase.

You get all whacky stuff too. My track bike has long (420?) chainstays and massive toe overlap. I betcha there are bikes out there with similar wheelbases and completely different characteristics. I guess what I'm driving at is that I don't reckon it's got a whole lot of predictive values as these measurements go.


* Teschner claim 950mm for a small Track 703, Surly claim 1100 for a big big Long Haul Trucker; I think those two are fairly close to the extreme on either end...

Krank
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Re: Bike Performance on Wheelbase

Postby Krank » Sat Nov 03, 2012 11:18 am

Intresting repsonse - thanks.

I am thinking of buying the Bianchi Infinito frameset instead of the Sempre.

The wheelbase is around 1.25cm longer in the same size frame, and I am wondering what difference (if any) this difference in wheelbase would make?

Krank

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greyhoundtom
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Re: Bike Performance on Wheelbase

Postby greyhoundtom » Sat Nov 03, 2012 11:33 am

Krank wrote:Intresting repsonse - thanks.

I am thinking of buying the Bianchi Infinito frameset instead of the Sempre.

The wheelbase is around 1.25cm longer in the same size frame, and I am wondering what difference (if any) this difference in wheelbase would make?

Krank

It depends entirely as to where the frame is longer.

Longer chainstays will soften the ride.
Longer fork offset reduces the sharpness of the steering.

Generally a shorter wheelbase will be better suited to racing on tight circuits, such as Criterium racing, while a longer wheelbase will provide better comfort on longer journeys.

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jonbays
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Re: Bike Performance on Wheelbase

Postby jonbays » Sat Nov 03, 2012 12:06 pm

Wheelbase but mostly fork trail or the castor of the front wheel play an important part in deciding the frames handling properties. If that 1.25 cm is all in the extra trail of say really curvy versus very straight front forks then the bike will be very directionally stable but not easy to turn in or lean into corners or very responsive. Also if you like to stand up and mash the pedals up a hill you waste more energy wobbling the bike side to side than you would with less trail. If the extra 1.25cm is in rear stay lenghth the ride quality on rough roads would be improved and again the turn in responsiveness slightly worse.

Krank
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Re: Bike Performance on Wheelbase

Postby Krank » Sat Nov 03, 2012 12:19 pm

thanks.

I will locate the profile for each frameset and post them here for your comment.

Krank

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Re: Bike Performance on Wheelbase

Postby TDC » Sat Nov 03, 2012 12:59 pm

greyhoundtom wrote:Longer fork offset reduces the sharpness of the steering.

\


Have disagree with this bit.

Longer fork offset reduces trail which increases steering response. (if HTA remains the same)

Eg: HTA 73 deg, Fork offset 43 mm...Trail = 58 mm
HTA 73 deg, Fork offset 53 mm...Trail = 48 mm

http://yojimg.net/bike/web_tools/trailcalc.php

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Re: Bike Performance on Wheelbase

Postby Magnus » Sat Nov 03, 2012 5:52 pm

TDC is right - greater fork offset = reduced trail = increased steering response - but the main variable concerning steering response is HTA. A frame with a steep HTA (my Reynolds 853 frame has a HTA of 74.5 degrees) will steer more responsively in spite of the size of the trail or the fork offset (as long as these are not extreme).

Shorter wheelbase will also make climbing a little easier.

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Re: Bike Performance on Wheelbase

Postby Krank » Sun Nov 04, 2012 10:57 pm

http://www.bianchiusa.com/bikes/road/co ... -frameset/

http://www.bianchiusa.com/bikes/road/bo ... -frameset/

TDC - Here are the different geometries I am looking into for both the Sempre and Infinito 2013 models.

I cannot see wheelbase dims, maybe you can.

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Re: Bike Performance on Wheelbase

Postby TDC » Mon Nov 05, 2012 9:07 am

Doesn't appear to be there. You will have work it out with some right angle triangle maths. You know dimensions D, C & F. Wheelbase = (C^2- D^2)+(F^2-D^2)

These both have 43 mm offset forks (from google so has to be true). The infinito looks to be the stable all day bike. Slower steering, and taller head tube. Sempre is more aggressive.

Either would be awesome because they Bianchis. You need to decide what type of ride you want.

Anyway wheelbase is just one element of the whole system and how it all works only really come into play when the rider is on the bike. How your weight is distributed etc.

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