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Bike fit variables: No. 3 wheelbase

Stu Bowers
11 Oct 2018

The distance between your wheels will have a significant effect on how your bike behaves. Here’s how to get the measure of it

If you carry your dirty bicycle into your house and set it down on your nice clean kitchen floor, the distance between the centres of the two muddy patches on the tiles will be the wheelbase of your bike.

Simply put, a bicycle’s wheelbase is the distance between the centres of its wheels, and it can be influenced by two key measurements: rear centre (distance from centre of rear wheel axle to centre of bottom bracket) and front centre (distance from centre of bottom bracket to centre of front wheel axle).

The resulting figure plays a big role in handling. 

Steering opinions

‘A longer wheelbase will be more stable at speed, and more stable with a load, but slower to turn. Visa versa for a shorter wheelbase,’ says UK framebuilder Tom Donhou of Donhou Bicycles.

‘That’s why a tourer will have a longer wheelbase than a road bike, for example.’

That’s basic physics. A vehicle with a longer wheelbase will require a greater turning force to have the same steering effect as a shorter one.

A tandem takes more effort to steer but is very stable going downhill, while a crit bike will have as short a wheelbase as possible for increased agility. 

‘Wheelbase is one of the most powerful influences on bicycle dynamics,’ says Tom Sturdy, head of education at the Bicycle Academy.

‘If I want to know if one bike will feel more agile than another, comparing the wheelbases will tell me most of what I need to know.

‘It’s a sensitive dimension, which is why most road bikes fall within such a narrow band.’

A quick glance at the geometry charts for six of the most popular road bikes on the market (all size 56cm) reinforces Sturdy’s point.

The variance in wheelbase is just 7mm, from 983mm to 990mm. Which begs the question: would 7mm be enough of a difference for the average rider to even notice?

‘Yes, 7mm would absolutely be noticeable,’ Sturdy says.

‘On a road bike I would expect a 5mm change to be noticeable to most riders and the more perceptive riders should be able to say which way the difference was – shorter or longer. Some very experienced riders might notice a 2-3mm difference.

‘It also depends on where the differences come from,’ he adds. ‘You’d certainly feel 3-4mm difference in chainstay length.

‘That has a big influence on the efficiency of power transfer – small changes have an effect on how the rear twists under load.

‘The front centre is a longer measurement so it would likely take a 5mm change or more there to really feel it.

‘Front centre is more complicated because there’s an interaction with steering and trail that affects how much weight is on the front contact patch.’

Eminent US framebuilder Craig Calfee agrees. ‘A 5mm change in wheelbase is noticeable, but one can adapt to a change like that quite easily, so how much it affects the outcome for the rider really comes down to how well they adapt to the bike.’

He suggests it’s how wheelbase influences weight distribution that’s key, not the length itself.

‘Typically you want a weight distribution of 45% front to 55% rear, but consider two riders with the same height and inseam.

‘One loves to mix it up in the sprints, say, and the other loves fast descents. The sprinter will want a shorter wheelbase, getting him closer to 50/50 weight distribution.

‘Assuming both riders could fit either a 54cm or 56cm bike, by adjusting the stem lengths and headset spacers, the sprinter would almost always go for the 54 and the descender the 56.’

So, if you were having a bike built for you, would you dial in the wheelbase to suit your riding preference?

‘We don’t set out with wheelbase as a primary design input,’ says Sturdy. ‘We often have to start out with clearance for wheel size, tyre size, etc.

‘But I’d definitely check what wheelbase this would produce and make adjustments accordingly. The most useful way to consider wheelbase is in a comparative way.

‘If you’re happy with the way a particular bike rides and you want another to ride the same then aim for similar.’

Yet Donhou does have one final word on the matter: ‘A frame is the sum of all its angles and distances, so we shouldn’t get hung up on one measurement alone.’

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