Have a HED jet + 6 and 9 with GP5000 TL setup size 25mm, and the size of the tire look just fine for the width of the rim, so don't think there is an aero penalty to run the 25mm in the front with these wheels.

I am not planning on doing the TL version, I use latex tubes. I wonder if there is any dimensional difference between the TL and tubed versions....

What is the rim internal diameter, diameter a mid brake tracks, and max diameter? How much do you and your bike weigh, and what will the road conditions be like?

On average rims, the gp5000’s appear to be measuring 1mm over sidewall spec, vs 2mm larger for the 4000’s.

I am guessing you want 23’s, that will measure closer to 24.

I think that is a pretty good setup. My 25TT measured 29 something after a few weeks at pressure. May want to check again later.

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I was asking because so many people ride Jet +s on here ST. The IW for them is 21mm, the EW is 25mms. I ride both really bad and really good roads, it just depends. We have a weekly free, honor system, time yourself world champs TT series that rotates over 5 courses here in NH. If I know we are on bad pavement I lower pressure 10 PSI or so. I have never had a flat and have 2000+ miles on my race wheels, including 4 year old latex tubes (yikes!).

Hed used to recommend the 22C Attacks as the best aero match for the front Jet+ wheels, I was just trying to translate how that would move to the 5000s. From what I am hearing it sounds like my initial hunch of 23C front and 25 C rear will be the ticket. I was hoping that someone has measured them with calipers.

GP5000 (25's) inflated to ~85 on my Jet 6's measure out at 27.72 and 27.86.

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I spoke to HED a couple of months ago. They recommended 23mm 4000 II for front and rear based on their testing. Previously they had recommended the Attack/Force combination. They had not yet tested the 5000.

It's so hard to keep track of all this stuff. I just got some Jet 6+'s installed on my tri bike, first race with them will be this weekend. For some reason I thought I'd read on here that the GP4000 25's were the preferred tire for these, but apparently I was remembering incorrectly. I'm not going to change to the 23's for this weekends race, but like how much time are we talking here? If it's an Oly distance race, estimate bike split around 60 minutes, is the difference between 25's and 23's a couple seconds? Surely no more than that, right?

Very interesating. I got my Jet Black 9/disc at the end of 2017 and have the recommended Attack/Force tires. I have 25mm GP5K on my road bike with Ardennes Black wheels, and those tires are very nice. It probably makes sense now to move the TT bike to a 23mm/25mm combo of the 5K tires, or maybe 23/23.

WOW! I'm running an old pair of Bontrager Aeolus wheels (non-TLR) with 25mm TT tires... this is a scary thought for aero needs but on IMWI roads, I almost think its worth it for the shock absorption.

Am I totally off here?

Yea, 29mm is pretty piggy for a front aero wheel, as is the 27.8mm that was measured earlier in this string. The old Force that was recommended for the rear was 27.7 when stretched, so my guess is it may be a little portly for the front.

I think that narrower tires "ride feel" at least one size wider when mounted on the 21mm ID rims. Also you can still soften the ride with pressure. I think the "ride feel" is pretty subjective, I felt that the 22C attacks were perfectly acceptable on rougher roads, I have always had confidence in them. My sense is bike shops steer everyone into 25s or 28s these days without a lot of questioning about aero or rim shapes.

May I ask where for the TT's? I'm in NH and would love to do these.

Regarding tires, the 23 is a perfect match on the Heds. I run 23 front 25 rear.

Don

https://mightypemi.blogspot.com/

Plymouth area. It is very low key and ranges from 10 to 20 riders per night. Starts Tuesdays at 6:00. The course records are really fast and they keep track of your PRS on the spreadsheet.

I would be inclined to go 23c gp5000 on those rims up front. They will measure closer to 25, maybe a bit more if you run pressures very high. It will be perfect aero for those front wheels.

The rear is a toss up between 23c and 25c in my mind, depending on your weight. Aero losses will be minimal with a 25, and easily offset by better crr if you lower the pressures appropriately.

The wrench in the whole story is that data is starting to come out that the gp5000 may be LESS aero than the gp4000sii...