Changing 20" front wheels to 26" on tadpole trike?

Specifically on an HPV Scorpion FS26 as in https://www.hpvelotechnik.com/en/re...bent-trikes/scorpion-plus-26-trike-high-seat/

What I would hope for:

• One tire/tube size
• Greater choice of MTB tires
• Increased ability to climb curbs.

What might the downsides be, especially considering this trike's 22" seat height?

 

Agreed, A.D. One can imagine (or calculate) the lateral wheels stress of a 230 pound rider in a 40 pound trike making a near 90 deg turn in only 100 feet at 20 mph. Hint: the answer is a wheel-warping lot. I've heard the outside curve 20" front on my Catrike 700 beg for relief since the inside curve wheel is virtually unloaded & trying to get airborne while the rear 700 is squealing. Then raise the center of gravity for 24" or 26" fronts (probably highly discouraged by the manufacturer) and it becomes top heavy. Nah, I don't wanna suddenly find myself spinning out looking the wrong way into traffic.

 

You just got two engineers to answer your question. I would go with what they said! Wheel warp. Yikes!!!

 

re/"...two engineers..."

Yeah! Never even considered a wheel collapsing while going through a corner.

That simplifies my decision-making process a lot... -)

 

I mounted 24" wheels on the front of my KMX Venom. I had these wheels built with Velocity A23 rims and Saoim CX-Ray spokes and they came out lighter and stronger than the 20" wheels they replaced.

What I found was high speed handling was 100% better. Low speed Handling suffered a bit but well worth it.

No engineer here but the trike cornered on rails with the larger wheels and was slightly faster. Better aerodynamics as the seat was a bit more reclined and the Bottom Bracket was raised. Also the larger wheels rolled significantly better.

I have a training metric that I use for working on sustained power. Pretty flat with only 2000 feet of climbing in the 62 miles with most of that coming in just two climbs. I use this to compare the speeds of different bikes. This works pretty well as it is a out and back that runs east to west so wind usually cancels out. Today I set out to do a big gear sustained power ride. Easy to do on the Venom with its 145 gear inches.

I never guessed I would have such a fast ride. The fastest on the Venom with the original 20" front wheels was 13.9 average. After going with the 24" wheels on the front I managed 15.2 very happy with the speed gain. I finally replaced the rear Jetset wheel with a matching Velocity A23/Sapim CX-Ray spoked wheel. At the same time I went with a Capreo style hub with a 9-36t cassette. This change solved the power gap I had in 14-17 mph range. So, anyway back to today's ride.

The first five miles are a gradual uphill before hitting the first real climb. I used this time to warm up a bit gradually increasing my power. A big downhill followed by a mile long climb. I stayed in my 67t crank on the Schlumph HSD and would for the next 40 or so miles. At the turn around I pulled my Garmin out and was surprised to see a 16.4 average. A quick stop fueled by a Starbucks iced Frappachino and an Almond Joy then back out.

My riding partner is an old defensive end and this ride really plays into his powerband, so he played the rabbit staying just out in front keeping me motivated to work harder. Around mile 50 the cramps wanted to set in but I just kept the cadence low and fought them off. Mile 52 or so was the only real climb on the way back. My legs were about empty so I bailed down to the 27t and spun slowly to the top. I actually recovered a bit and was moving pretty well at the top.

From there, mostly downhill to the car and at this point I wanted to finish in less than 4hours and I managed 3:58 total time. 3:54 moving time 16.1 mph average and 2077 feet of elevation gain. But, I beat my best time on the Windcheetah of 3:55 by 1 minute.
http://app.strava.com/activities/147688085a

 

Well, I went and did it.

Initial impressions after about 30 miles of riding on three successive days;

• Rolls easier over the less-than-smooth surfaces that I frequent.
  
• Climbs curbs better: now I can climb a 6" curb instead of 4" and the 4-inchers are much easier.
  
• Less vulnerable to potholes. Corporate lawn, neatly mown: that nice level grass can hide some problematic holes.
  
• Greater directional stability. Could be spun as "less responsive", but I like it. With 20" wheels it was what I would call "Twitchey" - not a good thing for me. Now, if I want it to turn, I have to exert conscious effort. Left alone, it tracks straight.
• Speed: the jury is out. With the 2.5" WTB Mutano Raptors that are on there now, it definitely takes more watts to go a given speed than with the 20" Schwalbe 2" Big Apples. But I have those tires on there just because I had them laying around from my biking days and, once Amazon delivers the two 1.75" Schwalbe Marathon HS 420 Touring Bike Tires I ordered, I expect it to need a few fewer watts than with the 20" wheels.

All-in-all, it just feels "Right".

OTOH, if a wheel collapses cornering and I become road kill, it won't feel so good... But the wheels are built on the same hubs and with the same spoking as the Full Fat - so I am not so worried...

 

I think you made the right choice. I didnt find Schwalbe Marathns to be very fast, but the **** things last forever.

 

I have a 2" Marathon Plus with a mild knobbie tread on the rear because:

• The 2" Big Apple that was on there would lose traction too easily on grass/dirt hills.
• After getting a flat with a 1.5" cyclocross tire back there and riding who-knows-how-far on the flat, I wanted to minimize the probability of a recurrence.