Rad City Chainring advice to increase top speed! Help Please!

[BKing]

Jim, you mentioned needing a lower gear when in PAS 4 and 5 up hills. You also mentioned needing a higher gear for down hills to maintain pedal resistance. I assume you have a 2020 City. You just need the 46 tooth front chain ring for the down hill problem. But this will also make it harder to go up hills if you are in gear 1 and PAS 4 or 5 and already having trouble going up. There is a limit on these bikes for uphill performance unless you are really light. You probably can’t fix both problems so go ahead and fix the down hill issue. Everyone is different on pedaling speed, what one rider thinks is pedaling too fast is just right for a rider that knows about perfect efficiency which is faster pedaling than 90 percent of riders you see on the road. I would not go higher than a 46 tooth in hilly country. For heavier riders like me, we don’t need to pedal much going down steep hills, the total weight takes off like a rocket. I have hit 34 mph with no pedaling after 25.

 

[Geno929]

I think you've got this completely backwards. If you want to avoid spinning out/add pedal resistance in 6th or 7th gear, you need a front chainring with more teeth, not less.

That is exactly what I made this post about. The stock 42 tooth chainring, that used to be 46 tooth, is not allowing me to spin in 6th or 7th gear.

 

[EBJ]

It appears Geno has had a good grasp on the situation from the beginning and has been pursuing a reasonable solution in terms of his personal preferences if he can find a chainring with the correct BCD for the City with a couple of extra teeth. He may or may not need a new (longer) chain, and the chain MAY not stick up above the chainring bash guards enough to require replacement with new larger guards (might be tough to find something compatible with the crank arm), or use a pant leg strap/clip.

Jim on the other hand has been all over the place, and if he now wants to go to something like a 53 tooth chainring, he will almost certainly need a longer chain and the stock chainring bash guards will be way too low to do what they were intended.

 

[Geno929]

It appears Geno has had a good grasp on the situation from the beginning and has been pursuing a reasonable solution in terms of his personal preferences if he can find a chainring with the correct BCD for the City with a couple of extra teeth. He may or may not need a new (longer) chain, and the chain MAY not stick up above the chainring bash guards enough to require replacement with new larger guards (might be tough to find something compatible with the crank arm), or use a pant leg strap/clip.

Jim on the other hand has been all over the place, and if he now wants to go to something like a 53 tooth chainring, he will almost certainly need a longer chain and the stock chainring bash guards will be way too low to do what they were intended.

Thanks EBJ for the advice. I did order a 130 BCD 44 tooth chainring, but it was smaller (outside diameter) than the current 130 BCD 42 tooth chainring on my Rad City. I've been looking for a 130 BCD 44 or 46 tooth chainring that will allow me to pedal at a slower cadence (80 - 95 rpm) and maintain current speed. Gosh, I'm starting to sound like a punter! Have a great day!

 

[Sierratim]

Hmm Sierra, Not sure I understand everything you said. What does "spin out" mean?

"Spinning out" refers to pedaling as fast as you can (max cadence) yet wanting to go faster. The rider has reached the maximum speed they could in the gears they have. The implication is that with a bigger gear they could have gone faster in the same scenario.

It sounds like you're 'spinning out' at 23mph. A larger chainring would help with this, but as @BKing notes this will negatively impact hill climbing ability.

 

[Sierratim]

Thanks EBJ for the advice. I did order a 130 BCD 44 tooth chainring, but it was smaller (outside diameter) than the current 130 BCD 42 tooth chainring on my Rad City. I've been looking for a 130 BCD 44 or 46 tooth chainring that will allow me to pedal at a slower cadence (80 - 95 rpm) and maintain current speed. Gosh, I'm starting to sound like a punter! Have a great day!

So the crank bolts are correctly placed at 130BCD?

If the new 44t chainring was smaller in diameter than what you have you must have a ring with more teeth since the teeth are all spaced the same. I'd suggest verifying your tooth count before reordering.

 

[Jim Mass]

Jim, you mentioned needing a lower gear when in PAS 4 and 5 up hills. You also mentioned needing a higher gear for down hills to maintain pedal resistance. I assume you have a 2020 City. You just need the 46 tooth front chain ring for the down hill problem. But this will also make it harder to go up hills if you are in gear 1 and PAS 4 or 5 and already having trouble going up. There is a limit on these bikes for uphill performance unless you are really light. You probably can’t fix both problems so go ahead and fix the down hill issue. Everyone is different on pedaling speed, what one rider thinks is pedaling too fast is just right for a rider that knows about perfect efficiency which is faster pedaling than 90 percent of riders you see on the road. I would not go higher than a 46 tooth in hilly country. For heavier riders like me, we don’t need to pedal much going down steep hills, the total weight takes off like a rocket. I have hit 34 mph with no pedaling after 25.

Thanks for your response BKing. I have the 2018 City with the 46T crankset. I ride 95% on the flat for exercise. We have a 9 mile asphalt trail about a block away from cars that parallels a river. The city built it on top of the levy. that goes under all major streets and terminates near the Oceanside Marina in San Diego county.( we ride around the marina or surface streets that paralel the ocean than ride back up the trail to the trail head). It passes a large park with clean bathrooms about 8 miles east of the marina. Wonderful safe area to ride on. In PAS1 gear #7 or #6 (headwind) I can maintain 15-18mph. Going down under the major streets the up portion is very steep for maybe 150 feet. I stay in 7th, keep pedaling with lots of throttle easily climbing the short 4-6% grade reaching the top at 8-10 mph. Then I'm back on the flat with lots of pedal feel unless I downshift to build my momentum back up.

I cruise on the local 25 mph marked rodes In PAS 3 sharing the rode with the cars (no marked bike lane). PAS 3 keeps me up around 22 mph so I don't feel intimidated by the cars. They are surprised at how much speed I can maintain and how fast off the line that I am. Like you I coast down the hills and its nice to know how fast it goes . The neighborhood I live in very hilly. One hill named "Cardiac" by the walkers is a long 4-5% grade (8 long blocks). Starting at the bottom dead stop in PAS 3 gear # 4 I'm doing 15 - 18 mpg at the top. The bike easily handles the various hills in PAS 3 or 4 downshifting to # 4 or # 5 gear. I just stay out of PAS 4 & 5 on the flats as there is no speed increase. I figured out by trial and error those PAS numbers are just for going up hills.

I decided for now to not change out the chain ring because I don't know the consequences of doing so.

 

[BKing]

Good idea, I think it’s just the 2020 City that needs a 46 tooth unless someone needs more help getting up hills then just leave it stock. Sounds like you are having a blast the way it is! I don’t want mine to go any faster due to the kids around here that ride their bikes on the wrong side of the neighborhood streets and constantly turn their heads to look behind them. When they do that, their bike veers off track drastically. We also have 14 year old kids driving golf carts the wrong way in traffic circles. I never take my fingers off the brake levers.

 

[ExPatBrit]

I went with 3 inch tires on my Rover for the summer, I removed the stock 42T and installed a 46T to compensate for the lower circumference of the tire/ wheel combo.

I commute to work on my bike, It does make it more usable at the high end, 5th gear is more like 7th gear used to be .

I can pedal up to about 28 mph on the flat before my legs can't keep up.

 

[Jim Mass]

That is reason i wondered if I switched from a 46 T to a 52 T if my 5th gear would be like my 7th and I would have two more gears

 

[BKing]

And you would have two less at the low end so you end up with the same amount.

 

[BKing]

I went with 3 inch tires on my Rover for the summer, I removed the stock 42T and installed a 46T to compensate for the lower circumference of the tire/ wheel combo.

I commute to work on my bike, It does make it more usable at the high end, 5th gear is more like 7th gear used to be .

I can pedal up to about 28 mph on the flat before my legs can't keep up.

So the 4 teeth made quite a bit more difference than changing the tire size.
Did you program in the effect of the tire size change or does it have enough choices. Use a gps app on your phone for accurate mph if you can safely look at it while going fast. I don’t think a Rad can go 28 on flat ground with 46 teeth unless you are a high end athlete standing up pedaling.

 

[Jim Mass]

BKing. Good point about losing 1st and 2nd. In my case not an issue as I never except that one time ever been below 4th gear. The City is not a mountain bike. A City bike is used mostly flat (except if your in San Francisco then maybe one does need a 42T). The road bike guy I passed in PAS 2 gear # 7 easily re-passed me as he up shifted to his last higher gear. He had skinny 29 " tires. Bike weighed 22 pounds. He pulled away like he had a rocket engine behind him. I think I passed him because he was getting tired and his metal seat hurt his butt. While I was riding in luxury with my Thunderbuster suspension seat post, soft seat, and 63 pound frame with only 60 pounds in the tires. I love "cheater bikes" especially at my age.

 

[ExPatBrit]

So the 4 teeth made quite a bit more difference than changing the tire size.
Did you program in the effect of the tire size change or does it have enough choices. Use a gps app on your phone for accurate mph if you can safely look at it while going fast. I don’t think a Rad can go 28 on flat ground with 46 teeth unless you are a high end athlete standing up pedaling.

I didn't check it with a GPS but it matches the speed monitoring / warning radar sensors in my 25mph restricted neighborhood

It can hustle in 7th with a Bolton upgrade and the big magnet motor. The color KT LCD8H display allows more adjustment on wheel size. Should have mentioned that.

 

[BKing]

Which motor did you get? Stock or upgrade?

 

[ExPatBrit]

Which motor did you get? Stock or upgrade?

Upgrade from the stock 350/500W motor to the real 750W watt from Bafang

You can just see the stock Rad Motor in the background of the pic

 

[BKing]

Cool! So you have the torque of a geared motor plus a good top speed. To put that on a City would require a new wheel too right? Due to thickness of the motor.

 

[ExPatBrit]

Cool! So you have the torque of a geared motor plus a good top speed. To put that on a City would require a new wheel too right? Due to thickness of the motor.

I have a Rover, 30 minutes work to switch . On a city with a freewheel the rear frame sizing is wrong.

Not an expert but with a city you need a MAC/ GMAC motor.

The new RAD mission has the smaller wheel and the geared hub but it's fixed gear.

 

[nj1266]

I know I am late to the party, but I had a similar problem on a much cheaper Swagtron EB7+. Ended up replacing the rear cassette from 14-28 to 11-28 and the chainring from 44T to 48T. I didn't replace the chain at all. https://electricbikereview.com/forums/threads/changing-gears-chainring-on-swagtron-eb7.40389/

 

[Jim Mass]

I already discussed this issue with my bike "Wrench master". I have a 2018 City Step-thru with the 46T chainring. Not big enough. You need a 52 T. Unfortunately for me I would have to modify the frame to get it to fit. The key is to replace the Step=thru model with the one featured if I can talk my wife into riding this one and I buy the model like yours after my upcoming hip replacement. Then change that to a 52 T.

At age almost 77 next month I ride for exercise, 20-25 miles per ride. Most of the time I'm in what I call exercise mode (PAS 1) in 6th to 7th gear, averaging 15-17mph on the flats. I want the higher chain ring so that there is peddle resistance and want to ride 5th and 6th gear saving 7th when I want more speed. I'm averaging 125 miles per month the last 18 months. Just turned 2,400 miles. I absolutely love the bike.