I like to do road bike TTs and therefore a 25 mm front is the fastest tyre. Now I normally pair this with a 28 mm rear tyre, but has anyone gone for a 30 or 32 mm rear tyre while keeping a narrow front tyre like a 25 mm? Will this alter the rear height enough to affect bike fit or create any weird handling?
I’ve gained a lot of weight these last two years (from 67 to 80 kg trying to get away from disordered eating as I’m 186 cm tall) and I am noticing my bike is feeling a lot harsher as I have had to increase pressures due to the weight gain.
Wheels are 21 mm ID and 28 mm OD.
You might be better off with 30’s on front and rear and running lower pressure. If it feels “harsh” then chances are the surface you are riding on isn’t all that smooth, and a slightly wider tire with less pressure will serve you better (make you faster overall) than trying to save 3 watts from aerodynamics.
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Going to be way more than 3 watts going from 25 mm to 30 mm, could be around 10 watts.
10 watts from drag seems optimistic to me for 5mm width, but even so, you’ll have less rolling resistance with the 30mm. Worst case try it and if you hate it you have a spare tire for the rear, but my guess is you’ll feel like you’re floating on a cloud and want to keep it. =)
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Swisside state a 6 watt penalty putting a 28 mm 111 aero tyre on over a 25 mm on my wheel, so a 30 mm will probably push it up to 10 watts (and I only have standard gp5000 which will be even worse aero wise) and alter other properties like stall. I know it’s only 5 mm but as a percentage of system width its a lot.
There is less weight on the front so a bigger tyre isn’t as needed, I’m just wondering if anyone has gone extra large on the rear on a road bike. Rolling resistance gains on the rear (if I hit a rough patch) and maximum aero efficiency on the front. Race speeds are above 25 mph so it does matter. Ideal world would be new wheels and a 28 mm front.
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I used a 25/32 combo (26.5/33 as measured) on a Canyon Ultimate. I noticed nothing, though it could be that I am less sensitive. I had to use the 32 because 30mm wasn’t available at the time. I am also a lighter rider (65kg) and was running pressures around 70/60 front and rear.
I am not a racer however.
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That seems excessive for a rear wheel that is largely sheltered from most of the wind…
Front wheel. You are right in that the rear wheel doesnt suffer much if any penalty bring wider. I want to keep the front narrow but go wide on the rear for best of both worlds.
Perfect thank you. What made you keep the narrow front?
At what speed, and rim widths, is that for?
I need to wear the tire down. I ended up selling the bike before I did so. On my new bike I run 28/30 which comes out to 30/32 as measured running 50 psi.
But in general I wanted the tire up front for aero reasons, matching the wheel width.
Swissside or DT swiss wheels. As above this is 21 internal and 28 mm external. It would be wind tunnel speeds so 45 kph (although they didn’t actually specify which speed).
Do you average around 45 km/h on your rides? If not I’d reduce that 10 watts difference somewhat.
I do in a race hence why I am asking this question (average is probably closer to 43 kph but I will spend significant parts of a race going over 50 kph on a decline or tailwind section). I once did 10 miles of a TT in 18.53 minutes on a road bike due to a tail wind. We race on A roads so travel much faster for the same watts than our American counter parts.
If it was just training rides I would just go 30 front and forget about watts.p
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1,942.8 mph, wow seriously fast.
More seriously, unless you are soloing breakaways. You are in a significant draft when racing and the supposed watts savings will be far less.
Whoops sorry should be minutes.
Time trials are solo efforts so no drafting allowed (unless you fancy a DQ).
Do you guys not have road bike time trials?
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Time trials of any form are few and far between these days in the US. They are out there, but very few sanctioned events (at least around me). I see a few non-usa cycling events that might include TT’s (often endurance stuff like 6, 12, 24h), but I just don’t see many that fit the traditional 40k (or similar) format. Wish there were more, I’ve got a decent engine and an old TT bike that just gathers dust.
So we have a class of time trialling that is just for road bikes. This is the fastest bike and rider in the UK at the moment (George Fox). I love this type of optimisation so just wanted to know if I could get the rolling resistance benefits on rougher roads at the rear (and comfort for normal riding) while still have aero efficiency at the front using slightly more extreme tyre size differences than you typically see.
I hate this type of optimisation! As the whole point of introducing a road bike category in TTs was so that people could just rock up and be competitive (equipment wise at least) on the same bike they already own for doing crits or road races. Thus making the sport more accessible to more people. Figuring out how to basically achieve TT bike speeds within the letter of the road bike rules by building a frankenbike like this is the exact opposite of what the road bike category was supposed to achieve.
Getting very off topic though! FWIW I agree with you that everything I hear from the aero experts continues to support a narrower tyre up front still being optimal for TTing on reasonably decent tarmac with no draft. And the companies that specialise in this stuff like Swissside, DT Swiss and Aerocoach are still making front wheels optimised for ~25mm for exactly this reason.
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