Maxxis Assegai F&R in the stickiest rubber and widest width thatāll fit your frame.
Already suggested and discarded due to gravel bike and 47mm max width.
Maxxis gravel tires. Keegan should be GOAT for even racing on Maxxis.
IRC tires. Pete would probably win more if he wasnāt sponsored by them.
WTB. God awful slow
Have fun.
A lot of the Touring tires on BRR that are slow are like 10 years old so maybe not made anymore but this Goodyear tire is recent and makes the Refuse and Gatorskin look fast by comparison.
The crazy thing is they donāt even offer good puncture resistance or wet grip, just bad lol.
Speaking as the slow spouse, getting an ebike was an absolute game changer when it comes to riding together. We are both so much happier!
Was thinking of writing a post about it as I know it can be tricky to discuss as the faster spouse. As nice as Mr. F has been about our power differential Iām not sure how I would have taken a suggestion of buying myself an ebike from him. If my perspective would be helpful for anyone considering an ebike Iāll gladly do a write-up. I bought a Specialized Creo Evo.
Yeah, my wife probably would have had similar thoughts. The suggestion to try an e-bike came from a friend while my wife was struggling with recovering from an injury (now healed, but the e-bike wonāt be going anywhere). I wonāt be surprised if another e-bike is in her future, maybe a mountain bike next.
The refuse are slow rollers so you could start there
And then thick thorn proof tubes as well. Could also consider a Mr tuffy type tire liner. Can also put slime in the tube.
I think 25-30 watts of additional rolling resistance per tire could be possible, making you pedal at 160 while she is at 100. It still might not be enough though, depending on yāallās fitness.
I tried this but ended up with her on an e-bike as well because she likes 15mph and not any more. 15 was a little too much work for her on her analog bike but with the e-bike itās fine. With my slow tires 15 is fine with me too.
Turns out the e-bike is really good for getting thru intersections and up short little steep hills that also were a problem on her analog bike. She likes being the faster rider when we go instead of always slower. The e bike for her plus slow tires for me has really made it nice for both of us.
Joe
Unless your wife is only 15-30 watts slower, then tires arenāt gonna do anything, and if she is only that much slower, just pedal slightly less hard? It seems more likely that you are a trained cyclist and she is not, in that case we are talking 100w or more. The only way you are gonna do that easily is just riding a different bike. If you have a MTB or fat bike, ride that, if not. Build up a 90s Steel MTB, you can find a million of these on Facebook or Pink BIke or wherever for like $200-300 bux. 26 in tires w/ tubes, flat bar etc. It will also be a lot more fun than riding studs or something weird. Better yet, get a single speed. Then youāll really be working lol.
I think the easiest factor to slow you down which is the biggest resistance you face when riding is aerodynamic resistance, some weight might help uphill but you will notice aero resistance uphill, downhill, and flat. If you want it to not stand out too much some things you might do is get yourself a nice big handlebar bag but you could also attach something to other parts of your bike if you want some real resistance.
Gator Skins! Had to use em in Philly thanks to all the glass and debris on the roads, it was SHOCKING how much faster a regular set of road tires was once I got to switch! 
Can you fix your brakes so they rub all the time? Get some mud on the tyres and bake it in to rub against frame as well.
Lots of resistance available from a Turbospoke, and your wife and other trail users will just love that sound:
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Look good on road & gravel bikes too!
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I have a fat bike and I use that once in a while when riding trails with my wife (she has a gravel bike or a mountain bike but uses her gravel bike mostly) and believe me that can be a work out. lower the tire pressure if you really want to work.
A Schwalbe Pro one was pretty slow tonight but that had something to do with a loose hub and the wheel rubbing against the chainstay.
Itās probably not relevant but I ride my MTB when I go road riding with my GF - we tend to average 27kmh which is a pretty good endurance pace for me on the MTB! Shes like 50kg so she smokes me on climbsā¦ She only cycles a handful of times a year though as its always raining here in Ireland. Anyway - works out well that way I think I wouldnāt enjoy it as much if I had a road bike.
Get a steel hardtail like a nuke proof scout with Enduro tyres - that should probably cost you a good bit of watts.
What about your old car tire?
In Norway there is sort of a trend with people doing tire-pulling on the gravel roads. This was originally used to train for expeditions and stuff but more and more ānormalā people keep doing it. Apparantly it gives a better workout for the posterior chain in addition to the obvious aerobic strain. I recently met three nice 60-ish yeart old ladies out there walking around with their tires 
This could be used on a bike
Anybody ever try giving a bit of a tow to your spouse up climbs using a tow strap? Something like the kommit? How was it?
Could be a bit dangerous
A tandem would be better